Three dimensional (3D) printing or additive manufacturing holds enormous promise as a manufacturing technique because it replaces the tooling necessary for conventional techniques with a CAD/CAM system directly driving the fixing of material into an object defined in the CAD file. All of the basic approaches to 3D printing are designed to use a single type of material for any portion of an object, and for any object created with the printer. The class of printers employing the technique known as fused deposition modeling (FDM), come closest to enabling the use of multiple materials. FDM machines use filaments of material that can be melted and extruded through a computer controlled print head, and then solidified shortly after the material leaves the extruder, to form a build-up according to the design in the CAD file. By employing more than one print head, each with a different type of filament, models of more than one material may be created. While these different filaments do represent different types of polymeric materials, the technique is limited to low melting point, largely organic materials.
Because FDM printers require the print head to trace every voxel in a 3D model, one voxel at a time, and at rates compatible with melting and extruding material, they are quite slow to produce an object of any significant volume. Because of this, FDM printers are used primarily to create models or prototypes.
3D printers based on binder jetting hold the greatest promise in terms of flexibility in the materials that are usable, and in the potential for increasing productivity substantially over other types of 3D printers. Binder jetting based 3D printers us an ink jet type printer head to spray glue onto a thin layer of powder, which, when set, forms a solid sheet of glued together powder, in the configuration defined by the pattern the computer dictated to the print head, for a given layer of an object. After the glue is set, a next thin layer of powder is spread over the original layer, and the patterned jetting of glue, or binder, is repeated in the pattern for that layer. After each layer is thusly patterned, the work piece is indexed away from the print head sufficiently to leave the relationship between the ink jet and the powder bed the same as it was for the first layer. The powder that was not patterned with the binder, remains where it was originally deposited and serves as a foundation for powder/binder sections deposited in areas not previously patterned with binder, and as support for the powder/binder structure. When deposition of the part is complete, the powder not patterned with binder is removed.
Current systems use powders ranging from plaster of Paris, bound with water for physical prototypes, to sand, bound by a glue for sand casting cores, to metal bound with glue, and subsequently sintered to a finished metal part. None of the current systems are capable of creating an object with different regions of the object comprised of different material.